A sound decoupling connecting element of the type described above is known from the U.S. Pat. No. 5,094,579. The connecting element serves to connect two parts with a gasket inserted inbetween. The connecting element itself has a screw, a washer, and a formed body of elastomer material, especially rubber; the connecting element therefore consists of three parts. The formed body of the connecting element has a central opening and a flange, which comes to rest on the outer surface of one of the two parts to be connected. The formed body has a continuation, with which it extends into an opening in one of the two parts to be connected. It has on its outer circumference a recess, with which it can be snapped into the step of a stepped bore hole in the first part. The free end of the continuation then lies between the two surfaces of the first of the two parts to be connected. The formed body has an opening in its center, through which the screw passes. Approximately in the intermediate region between the threaded part of the shaft of the screw and the threadless part of the shaft of the screw a radially outwardly extending collar is provided, the outer diameter of which is designed so that it passes through the opening in the formed body with a certain amount of clearance. At the end of the formed body, at which the washer rests, that is located at the head of the screw the formed body has a stop, which works together with the collar of the screw acting as a counterstop in such a way that the screw has limited axial movement relative to the formed body and all three parts are kept together as a premounted unit, so that the screw is held in an unlosable way at the formed body. The conecting element consisting of screw, washer and formed body can therefore be delivered premounted and as one unit. It is then merely necessary to clip the formed body of the unit into the step-like opening of the first part and finally to tighten the screw. As a premounted unit as well as in the position attached to the first part the screw is held to the formed body unlosably but only loosely, so that the screw has an undefined position with respect to the formed body. This is especially the case with overhead or slanted mounting positions. The screw can tilt with its axis within the formed body and relocate itself depending on its relative position to the axis of gravity. When screwing the screw into the thread, which is located in the second of the two parts to be connected, the screw penetrates a gasket with its tip and the threaded shaft. This not only has the disadvantage that components of the gasket can enter the thread and hinder or prevent the further screwing-in process; it is even more disadvantageous that in the course of this the middle collar on the shaft of the screw settles on the penetrated gasket and compresses this. The result of this is a nonreproducible and undefined end-mounted position, in which the screw holds the two parts to be connected more or less together and also compressses the formed body. During this compression the stop on the formed body, which sets the lift of the limited axial movement of the screw relative to the formed body, comes to rest on the shaft of the screw, so that a seal is achieved here, which makes it possible to use the screw in an area enclosed by the gasket. On the other hand there is the possibility that the collar provided in the middle region of the shaft of the screw supports itself on the surface of the second of the two parts to be connected. For this the gasket would have to be provided with an opening corresponding to the outer diameter of the collar, though. In this embodiment a reproducible end-mounted position is attained, in which on the one hand a reproducible prestress can be applied on the screw by the dimensioning of the different parts and on the other hand the formed body is reproducibly compressed and therefore clamps together the two parts. In both embodiments there is no possibility to create a premounted unit in which one of the two parts to be connected, the different connecting elements used, and the gasket form a premounted unit. Such a premounted unit including the gasket could only be created by further developing the gasket and providing it with an opening for the screw of each connecting element, the diameter of which is dimensioned so that it can engage in a turned groove between the collar and the threaded shaft of the screw. Further developing the object of the U.S. Pat. No. 5,094,579 in this direction results in two disadvantages: For one thing the limited axial movement of the screw relative to the formed body is lost, and for the other thing reproducible end-mounted positions cannot be obtained. Apart from this the connection with the gasket would be lost when the connecting elements are loosened.
A connecting element premountable to one unit from three parts, which does not furnish a sound decoupling effect, though, is known from the EP 0 272 642 A2. The connecting element is comprised of a head screw, a sleeve with a collar, and a formed body made of elastomer material. Between the sleeve and the screw stops and counterstops are formed here also, with the aid of which the screw is arranged unlosable and with limited axial movement. The sleeve is inserted into an opening of the formed body. This can be done with an anchoring in one of the two parts to be connected with each other. A gasket between the two parts to be connected to each other is not provided, so that the two parts are directly fastened to each other with their facing surfaces. In the process of this the sleeve can rest and support itself on the surface of the second of the two parts to be connected, so that through this sleeve a reproducible compression of the formed body is attained. The stops on the screw are formed by protruding cams, over which a stricture of the collar of the sleeve can snap when the two parts are connected. Here, too, the lift of the limited movement is set by stop and counterstop. Apart from this the screw can be tilted relative to the sleeve according to the given clearance, so that it is not guided with respect to the counterthread in the second of the two parts to be connected. An overhead mounting is also made difficult insofar as the screw, when let go of, will move the distance allowed by the limited lift in the direction dictated by gravity. The collar on the sleeve extends in a radial direction in such a way that its outer diameter is flush with the outer diameter of the formed body, while the head of the screw carries a normally dimensioned head bearing area. By way of the collar of the sleeve the compressing force of the screw is then transferred to the formed body. The creation of a connecting element from three parts represents here, too, a corresponding expenditure.